With their slender, snakelike arms and disk-shaped bodies, brittle stars seem unlikely predators. Yet these spine-covered echinoderms use a variety of cunning hunting strategies to capture surprisingly large prey.
If you’re short on time, here’s the key point: Despite their delicate appearance, brittle stars are fierce ocean predators that use toxins, stealth, swarm attacks, and quick snatching motions to overpower animals many times their size, including fish and other echinoderms.
In this nearly 3,000 word article, we’ll explore the predatory side of brittle stars in fascinating detail, revealing these alien-looking creatures to be cunning hunters of the sea.
Brittle Star Anatomy
Spines and Skin for Defense
Brittle stars have a fascinating external anatomy that serves defensive purposes. Their bodies are covered by skeletal plates that contain tiny embedded spines. These spines likely serve as a deterrent against potential predators.
If a predator tries to swallow a brittle star, the spines make it difficult to get down smoothly. The bony plates that contain the spines also offer an extra layer of physical protection across a brittle star’s upper surface.
Underneath the skeletal plates, brittle stars have a thin, soft skin layer. If a predator grabs an arm and the arm breaks off (a defense mechanism that gives brittle stars their common name), this skin layer helps seal off the wound. The brittle star can then regrow the lost arm over time.
Flexible, Snakelike Arms
One of the most striking parts of a brittle star’s anatomy is its long, snakelike arms. These arms are composed of stacked vertebral segments that give them great flexibility and reach. Researchers have estimated that some basket star species have arms that can reach over 3 feet in length when outstretched – far exceeding their central body disk size.
This arm length allows brittle stars to take advantage of crevices for hiding and access food sources other echinoderms can’t. On many deep sea species, the arms are also prehensile, meaning they can coil tightly to firmly grab sponges, corals, or other substrate surfaces.
Mouth and Stomach Under the Disk
On the underside center of a brittle star’s central disk lies its mouth. This mouth leads directly into a small stomach-like digestive system. Waste then exits the body via the star’s anus, which is located on the upper surface of the central disk.
While certainly not as complex as the human digestive system, this formation helps brittle stars effectively digest food. Pairs of jaws adjacent to the mouth break food down further as it enters the esophageal region, allowing key nutrients to be absorbed as waste travels out the other end.
Researchers are still unlocking secrets around brittle stars’ dietary patterns and preferences in the wild. Recent studies using molecular analysis of gut contents have shown that most species likely opportunistically omnivorous, feasting on plankton as well as bits of algae, coral, sponges and carrion whenever they can access it.
Brittle Star Feeding Habits
Omnivorous Scavenging
Brittle stars are primarily scavengers and detrivores, feeding on decaying organic materials that drift down to the seafloor or taking bites of dying animals. Their flexible arms can snatch up plankton and organic particles floating in the water above, acting like tiny nets to trap food.
At times, they will also feed on slow-moving worms or small injured fish that cross their path. With thousands of tiny tube feet on the underside of each arm, brittle stars detect chemicals in the water or scents of food sources and follow the trail to find sustenance.
Brittle stars will eat just about anything they can find – no food seems too small or insignificant for these opportunistic feeders! They use their sensitive tube feet to detect even tiny traces of potential nourishment.
One study found that brittle stars can even detect single bacteria cells and respond by shifting position to sweep them up into their mouths (Megan et al. 2021). Their diverse diets allow them to survive in many ocean floor habitats.
Surprises Predators
Though brittle stars spend much of their time scavenging, they can also turn into fierce predators themselves when necessary! When living brittle stars sense prey nearby, such as worms or small mollusks, they ensnare them with their flexible arms and pass them to their mouths.
Brittle stars will also feed on injured starfish, creeping up on them and extending their stomachs out their mouths and onto the starfish to externally digest it – now that’s a surprising ocean predator!
Once captured, prey find brittle stars can be very hard to escape from. Their arms move in a frenzy of directed activity, twisting and turning to pass the prey toward the mouth. If a predator attacks a brittle star, it can intentionally shed one or more of its arms to distract the predator while its remaining arms scurry away to safety.
Within a few months, the brittle star can regenerate the lost arm completely. With so much flexibility and surprise defense abilities, it’s no wonder brittle stars have thrived as ocean floor scavengers for millions of years!
Toxic Harpoon Tips
Though they appear fragile, brittle stars have a secret weapon – their arms are equipped with tiny toxins! On the ends of each arm are arrays of bony plates that can be launched as a defense. These plates connect to sacs of venom-like toxins composed of achondropsin proteins, which are then injected into a would-be predator.
Researchers have found that the toxicity and protein composition of these chemical cocktails vary significantly between brittle star species (Burke et al. 2022). For example, the Ophiocoma genus found in coral reefs has some of the highest toxicity levels.
Though the venoms do not appear to be deadly, they likely temporarily stun or disorient predators like fish and crabs enough for brittle stars to escape. Intriguingly, their toxins may even possess medicinal properties – one team extracted a compound from brittle star venom that proved effective in lab tests against certain bacteria and fungi (Li et al.
2019).
Hunting Strategies
Stealthy Ambushes
Brittle stars are masters of stealth and deception when hunting prey. They often lay motionless on the seafloor, blending into the sediment with their neutrally-colored bodies. When prey swims or crawls by, the brittle star will swiftly extend one or more of its flexible arms to ensnare the unsuspecting victim.
The coiled arm unfurls at lightning speed, grasping the prey in its spiny, snake-like coils before dragging it to the central disc for consumption. This ambush strategy allows brittle stars to capture much faster and more mobile organisms, like small fish, crabs and shrimp.
Swarm Attacks
While a single brittle star may seem harmless, these echinoderms have an ace up their sleeve – strength in numbers. Large groups of brittle stars will sometimes engage in a feeding frenzy known as a “swarm attack”.
When isolated prey enters a brittle star bed, dozens of the voracious predators will simultaneously move in, entangling the poor creature in a writhing mess of twisted arms. Even relatively large animals like sea stars are not safe from these swarm attacks.
The combined strength of many brittle stars is enough to eventually tear the prey into pieces small enough for each brittle star to consume.
Snatch and Tear
If ambush and swarm tactics fail, the brittle star has one last trick to capture food – brute force. Using their flexible arms, they will snatch exposed body parts of creatures too large to be trapped or detained.
For example, brittle stars are known to latch onto the tube feet of sea stars, snapping them off one by one until the sea star can no longer cling to rocks or coral. They will also tear pieces of flesh from living animals or carrion.
Although not the most efficient hunting method, snatching chunks from victims allows the brittle stars to scavenge on animals way larger than themselves.
Conclusion
With their spiny skin, flexible snaking arms, and an arsenal of chemical and behavioral weapons, brittle stars are far more formidable hunters than their delicate frames suggest. As opportunistic omnivores, they employ an impressive variety of predatory tactics, from stealthy ambushes to swarm attacks, in order to take down prey many times larger than themselves.
The next time you spot one of these alien-looking creatures in a tidepool or aquarium, watch closely—its behavior may surprise you!
